- Letter to the Editor
- Open Access
ME (Ramsay) and ME-International Case Criteria (ME-ICC): two distinct clinical entities
Journal of Translational Medicine volume 18, Article number: 447 (2020)
The review of the differences and similarities in the different case definitions for myalgic encephalomyelitis (ME)/chronic fatigue syndrome (CFS) by Lim and Son  deserves appreciation. Based on their analysis the authors acknowledge the “distinct view of ME and CFS”  and recognize four categories of case definitions: ME, ME/CFS, CFS  and Systemic Exertion Intolerance Disorder (SEID) .
Indeed these labels reflect very different case definitions . According to Lim and Son  the first category comprises two ‘ME’ case definitions: ME (Ramsay)  and ME according to the International Case Criteria (ME-ICC) . However as can be deduced from Table 2 , ME  and ME-ICC  are two distinct clinical entities .
ME (Ramsay)  is a neuromuscular disease. The discriminative symptom of ME is muscle fatiguability/prolonged muscle weakness following trivial exertion. Ramsay states : “[I]n my opinion a diagnosis should not be made without it”. Muscle fatigability is accompanied by “neurological disturbance, especially of cognitive, autonomic and sensory functions” . So, in essence the case definition of ME (Ramsay)  is very simple  and requires two (types of) symptoms: muscle fatigability/post-exertional muscle weakness and specific neurological symptoms. “Other characteristics include [..] a prolonged relapsing course and variation in intensity of symptoms within and between episodes, tending to chronicity.” .
In contrast, the ME-ICC case definition  is much more complex. The diagnosis ME-ICC requires post-exertional neuro-immune exhaustion (mandatory symptom), at least three symptoms related to neurological impairments; at least three symptoms related to immune, gastro-intestinal, and genitourinary impairments; and at least one symptom related to energy production or transportation impairments .
The case criteria of ME  and ME-ICC  define two very different patient groups. Muscle fatigability/long-lasting post-exertional muscle weakness, a hallmark feature of ME, is not required to be qualified as ME-ICC  patient. Symptoms indicating autonomic, sensory, and/or cognitive dysfunction, also mandatory for the diagnosis ME , are not required to meet the ME-ICC  ‘neurological impairments’ criterion. The diagnosis ME  requires only two type of symptoms (muscle fatigability/post-exertional muscle weakness and “neurological disturbance”), but the polythetic definition of ME-ICC  requires a patient to have at least 8 symptoms. In essence, the case criteria of ME (Ramsay) and ME-ICC are not interchangeable (Fig. 1) .
Finally, it is important to note that, in contrast with Table 2 , ME  is often but not always triggered by an infection and that ME requires at least four symptoms: muscle fatigability/prolonged post-exertional muscle weakness and three neurological symptoms indicative of cognitive, autonomic and sensory dysfunction.
In conclusion, ME (Ramsay) , a neuromuscular disease, is not comparable to ME-ICC . ME , ME-ICC , ME/CFS, CFS  and SEID  are distinct clinical entities with partial overlap. So solving the current confusion with regard to case definitions requires a clear distinction between ME , ME-ICC , ME/CFS, CFS  and SEID .
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All data related to this study are available in the public domain.
Chronic fatigue syndrome
Systemic Exertion Intolerance Disorder
ME as defined by the International Case Criteria
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This article is dedicated to Dr. Ramsay, Dr. Dowsett, Dr. Acheson and various others who dedicated their professional career to ME.
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Twisk, F.N.M. ME (Ramsay) and ME-International Case Criteria (ME-ICC): two distinct clinical entities. J Transl Med 18, 447 (2020). https://doi.org/10.1186/s12967-020-02617-0
- Myalgic encephalomyelitis
- Chronic fatigue syndrome
- Case criteria